The applicant is aware of the following U.S. patents, the disclosures of which are incorporated by reference herein:
U.S. Pat. No. 2,369,551 PA1 U.S. Pat. No. 2,964,003 PA1 U.S. Pat. No. 3,400,838 PA1 U.S. Pat. No. 3,516,316
Stock pushers or crowders are known in the prior art. These devices are designed to assist in the metal forming process by assuring that stock pieces are properly positioned against a reference surface within a metal forming machine prior to the start of a machine cycle. This assures that the metal forming process, whether it be bending, punching or cutting, is performed in the same manner and at the same position on each piece of stock that is inserted into the machine.
For example, a design known from U.S. Pat. No. 3,400,838 discloses a device which has a lever, a compression spring, a cam, and a pivotal arm. The lever and compression spring are mounted to the moving die shoe of the metal forming machine. The cam is attached to the pivotal arm, which, in turn, is attached to a stripper plate located immediately above the stock piece. The compression spring urges the lever in a lateral direction towards the cam and pivotal arm. When the machine lowers the die shoe into its operating position, the lever comes into contact with the cam. The lever then forces the cam and the pivotal arm to move towards the stock until the pivotal arm makes contact with the stock and forces it against a reference surface. When the metal forming operation is complete, the lever is raised, allowing the cam and pivotal arm to move away from the stock. This design takes up considerable space within a metal forming machine and, due to its two-element design, requires realignment between the lever and cam/pivotal arm anytime the device is moved or the machine setup is adjusted.
Similarly, U.S. Pat. No. 2,369,551 also discloses a device which uses a depending lever to contact the stock. The lever is biased by an external spring.
U.S. Pat. No. 3,516,316 discloses a different design. An arm is pivotally attached to a moving stripper plate within a metal forming machine. A torsion spring urges the arm to pivot downward towards the workpiece holder so that one end of the arm extends below the bottom surface of the stripper plate. The stripper plate and pivoting arm are moved downward when the machine tool is moved downward for operation. The end of the arm comes into contact with the workpiece holder before the stripper plate and is forced to rotate against the force of the torsion spring and towards the stock. Prior to the stripper plate engaging the stock, the arm makes contact with the stock piece and forces it against a reference surface. When the operation is complete, the tool and stripper plate are raised, allowing the pivoting arm to rotate away from the stock and back to its starting position.
Another design is illustrated in U.S. Pat. No. 2,964,003. The design of this stock crowder has a unit that mounts directly to the moving die shoe which holds the machine tool. The unit has a mount; a pivoting, L-shaped lever; and a compression spring. The shorter leg of the L-shaped lever extends horizontally away from a pivot point. The longer leg of the lever extends vertically downward towards the stock piece. The compression spring, contained within the mount, acts on the shorter leg of the lever to create a moment in the lever about the pivot point. This moment urges the longer end of the lever into contact with the stock. The lever then forces the stock against a reference surface. In this design, the mount and lever occupy considerable space within a metal forming machine due in large part to the L-shaped design of the lever. When the user desires to change the direction of force applied by the device, a separate mount and lever must be used and the moving die shoe must be adapted to accommodate a seat for the compression spring.